Biological catalysts including enzymes, bacteria, yeasts, fungi, algae, animal cells, and plant cells, have been utilized for many years to produce gene products, pharmaceuticals, biologically active compounds, biomass, primary metabolites, secondary metabolites, cellular components, proteins, etc. For such purpose, many different types of bioreactors and apparatuses have been employed to provide an adequate environment for those biocatalysts that is conducive to high productivity.
Typically such processes and apparatuses comprise mixing devices to provide good contact between biocatalysts and reactants and uniform distribution of biocatalysts, substrates, and products within the bioreactor; mass transfer devices to provide and maintain an adequate supply rate of nutrients including oxygen or carbon dioxide, substrates or reactants to the biocatalysts, provide a good mass transfer of product; and control devices to provide and maintain optimal environmental and operating conditions for the best performance of the biocatalysts and bioreactors.
For most bioreactor systems employed for microbial and enzymatic processes, standard fermenters, typically stirred tank reactor, with those devices have been satisfactorily used for many years. However, with the recent advent of biotechnology, there is an urgent need for new types of bioreactor systems specifically designed for and applicable to animal and plant cell cultures that are more delicate and sensitive to shear and other physical and chemical environmental conditions as compared to the microbial fermentation systems.
The present invention provides a novel type of bioreactor system that can be used advantageously for cultivating delicate cells like animal and plant cells and protoplasts. It also provides a novel type of bioprocess by which useful products can be made and can be recovered and/or separated simultaneously by using such a bioreactor system.
It is well recognized that several problems need to be overcome for the development of a large-scale bioreactor system and for its satisfactory operation when delicate biocatalysts are to be employed and/or cultivated. Among the critical problems to be overcome and resolved are: (A) Providing adequate mass transfer rate: Supply of oxygen and carbon dioxide to the animal and plant cells without causing any damage to the cells by high shear rate caused by the mass transfer devices and operations. (B) Removal of toxic metabolites that inhibit the growth and production of desired products especially when more than the critical amount of those toxic metabolites is accumulated in the culture medium. (C) Providing adequate strategy for the process monitoring and control based on the understanding of fundamental cellular genetic characteristics, metabolism, and physiology.
With a view to overcoming some of these critical problems in biotechnology, we have developed a novel type of bioreactor system and a set of conceptual process schemes by which it can be operated effectively to produce many different bioprocess products including gene products especially from plant and animal cells.
The present invention overcomes the major disadvantages of the prior art. It provides a significantly improved type of bioreactor system design, where sufficient mass transfer rates of nutrients including oxygen can be provided without causing any physical and/or shear damage to the biocatalysts by separating the mass transfer zone (or stage) and production zone (or stage) in a single continuous staged fluidized-bed bioreactor system. It further provides a bioprocess technology where continuous biologically catalyzed reactions are carried out over a wide range of operating conditions without losing or destroying a significant amount of biocatalysts for a prolonged operating period.
The invention provides continuous and simultaneous production and recovery of bioproducts by supplying sufficient amounts of nutrients and reactants, removing toxic metabolites continuously and recycling valuable nutrients, and selectively separating the products continuously. It also provides effective monitoring and control of important process variables for the purpose of optimal control and economic processing.